The present invention relates to transmitters of tire condition monitoring apparatuses, and, more particularly, to transmitters attached to wheels, to which tires are connected, for transmitting data indicating the condition of the tires, such as air pressure, to a receiver installed in a vehicle.
A wireless tire condition monitoring apparatus has been proposed to enable a driver to monitor the condition of a tire of a vehicle in a passenger compartment.
With reference to FIG. 4, the tire condition monitoring apparatus includes a transmitter 50 for transmitting data indicating the air pressure of the tire to a receiver (not illustrated), which is installed in the vehicle. The transmitter 50 has a square box-like casing 51 and a valve stem 52, which is formed integrally with the casing 51. The casing 51 accommodates an electronic board 53 and a battery 54. A communication hole (not illustrated) is formed in the casing 51.
The electronic board 53 is substantially square. Two bosses 55, 56, which are integrally formed with the casing 51, fix the electronic board 53. The bosses 55, 56 are located at diagonal positions in the electronic board 53. The electronic board 53 is provided with circuit elements 57, such as a pressure detecting element and various signal processing elements. A battery 54 is connected to the electronic board 53 for supplying power to the circuit elements 57.
With reference to FIG. 5, the casing 51 of the transmitter 50 is fitted into a valve hole 63 of a wheel 62 such that the casing 51 is located in the interior of a tire 61. A valve stem 52 introduces air to the interior of the tire 61 through a communication hole. The valve stem 52 also functions as an antenna that transmits the data indicating the air pressure of the tire 61.
The casing 51 is formed of resin to reduce the weight of the transmitter 50. When the vehicle is moving, centrifugal force acts on the transmitter 50, which is attached to the wheel 62. The centrifugal force is generated in relation to the outer diameter of the wheel 62, the outer diameter of the tire 61, and the traveling speed of the vehicle. For example, the centrifugal force is approximately 1,500 G when the vehicle traveling speed is 300 km/h. The centrifugal force deforms the casing 51 such that the positions of the bosses 55, 56 relative to each other are changed. This generates force, which acts on the electronic board 53. The electronic board 53 is also affected by the centrifugal force, which is caused by the movement of the vehicle. The electronic board 53 is thus deformed by these forces. This applies excessive force to the circuit elements 57, thus damaging the circuit elements 57.
The valve hole 63 of the wheel 62 is formed such that the valve hole 63 is inclined with respect to the rotational axis of the wheel 62 at a predetermined angular range (17.5 to 20.0 degrees). Also, the position of the valve hole 63 may be varied among products. Thus, the inclination angle of the valve stem 52 with respect to the casing 51 needs to be selected such that the casing 51 does not contact a drop center portion 62a of the wheel 62 when the transmitter 50 is attached to the wheel 62.
If the inclination angle of the valve hole 63 with respect to the rotational axis of the wheel 62 is relatively large, the casing 51 is spaced from the drop center portion 62a of the wheel 62 at a relatively large interval when the transmitter 50 is attached to the wheel 62. Thus, if a bead portion 61a of the tire 61 contacts the casing 51 when the tire 61 is being attached or detached from the wheel 62, force acts on the casing 51 to urge the casing 51 toward the drop center portion 62a of the wheel 62. With reference to FIGS. 6(a) and 6(b), the force deforms the casing 51, as indicated by the broken lines. This deforms the electronic board 53 and thus damages the circuit elements 57.
Accordingly, it is an objective of the present invention to provide a transmitter of a tire condition monitoring apparatus that prevents a circuit element from being damaged.
To achieve the foregoing and other objectives and in accordance with the purpose of the present invention, the invention provides a transmitter of an apparatus for monitoring the condition of a tire of a vehicle. The transmitter includes an installed portion, a casing, and an arm. An element for detecting the condition of the tire is installed in the installed portion. The casing accommodates the installed portion. The installed portion is connected to the casing by the arm. The arm tolerates reactive force acting on the casing and protects the installed portion from that reactive force.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.